The present invention relates to the continuous casting of metals in molds and more particularly to the casting of metals in molds formed by closing the peripheral groove of a rotatable casting wheel with a continuous flexible band, and to a method and apparatus for starting the casting of such metals.
In the casting of molten metal in the mold of a casting wheel, particular problems which arise when the molten metal is first introduced into the mold must be overcome. One problem is that the shock of the heat transfer from the molten metal to the material of the relatively cool casting wheel and flexible band is significant and can cause substantial deterioration of these materials.
In order to minimize this deterioration, continuous casting wheels are generally cooled using a liquid coolant which is applied to some or all of the exterior surfaces of the mold. However, if the molten metal surrounds any liquid coolant adhering to the interior surface of the mold to form a pocket of coolant, the heat of the molten metal will quickly vaporize the coolant and cause the resulting gas to expand so rapidly that the pocket which has been formed will literally explode and propel molten metal from the mold.
Therefore, in spite of the requirement for maximum cooling of the mold to prevent deterioration of mold materials, it is necessary to postpone full volume cooling of the exterior of the mold until just after the molten metal has begun to be poured into the mold so as to avoid pockets of coolant. A method of low volume preliminary cooling is described in U.S. Pat. No. 3,596,702, issued to George C. Ward on Aug. 3, 1971, and has been effective to minimize thermal shock and deterioration problems in the continuous casting of metals having relatively low melting points, such as copper, aluminum and lead, while at the same time minimizing the possibility of explosive reactions between the molten metal and coolants splashed into the mold. The disclosure of said patent is expressly incorporated herein by reference.
In the casting of metals of relatively high melting points, such as steel, the problems of starting continuous casting in a casting wheel are greatly magnified. The temperature of molten steel, for example, is not only high enough to cause heat deterioration to the mold, but is normally above the melting point of the constituents of the mold since the casting wheel is normally constructed of materials which have high heat conductivity to allow efficient cooling but which tend to have relatively low melting points.
Furthermore, the high temperatures of these metals in their molten state makes their contact with liquid coolant adhering to the interior surfaces of the mold an even more explosive and significantly more dangerous event compared to metals having a significantly lower melting point. Thus, the methods of preliminary cooling in connection with direct introduction of the metal to be cast which have been successful in starting the continuous casting of metals having relatively low melting points will not sufficiently protect the mold from the possibility of melting or heat deterioration, while at the same time providing a sufficient margin of safety for the operator or the equipment against the possibility of explosion if metals of significantly higher melting points are cast.